In large milking systems a large number of milking members are connected to the same milk tank for receiving and storing the milk from the different milking members. The milk from the different milking members is conveyed to the milk tank via a transport line. All milk passes through a milk filter unit before reaching the milk tank. The filter element or elements of the milk filter unit has to be replaced regularly, typically three times a day. It is preferred to replace the filter element just before the cleaning operation so that the cleaning operation can be performed with a clean filter element not influencing the cleaning liquid in a negative way.
EP-A-1 559 314 discloses a milk filter unit for a milking system. A cleaning equipment provides a rinsing liquid and a cleaning liquid during a cleaning operation via a transport line connected to the cleaning equipment. The milk filter unit is provided on the transport line and comprises a first filter device and a second filter device, each comprising a filter container and a filter element. A valve arrangement is configured to convey the rinsing liquid and the cleaning liquid through at least one of the first filter device and the second filter device. A control unit is provided for controlling the cleaning equipment and the valve arrangement. The control unit supplies, during the cleaning operation, the rinsing liquid through the milk filter unit and the first filter device during a pre-rinsing phase, the cleaning liquid through the milk filter unit during a cleaning phase, and the rinsing liquid through the milk filter unit and the first filter device during an after-rinsing phase.
One problem with the known milking systems is that it is difficult for the user to know whether a filter element needs to be replaced or has recently been replaced. In case of two filter devices, it can be difficult to know which of the filter elements needs to be replaced or which of them has been replaced.
It is also to be noted that the filter element must not be replaced when the milk is passing through the filter element. It is also not possible to replace the filter element during the cleaning operation when the cleaning liquid is circulating in the transport line and thus through the filter element.